West Tamar Highway, Cormiston Road to Legana (Legana Park Drive), Highway Duplication
Total Page:16
File Type:pdf, Size:1020Kb
2004 (No. ) 2004 _______________ PARLIAMENT OF TASMANIA _______________ PARLIAMENTARY STANDING COMMITTEE ON PUBLIC WORKS West Tamar Highway, Cormiston Road to Legana (Legana Park Drive), Highway Duplication ______________ Presented to His Excellency the Governor pursuant to the provisions of the Public Works Committee Act 1914. ______________ MEMBERS OF THE COMMITTEE LEGISLATIVE COUNCIL HOUSE OF ASSEMBLY Mr Harriss (Chairman) Mr Best Mr Hall Mrs Napier Mr Sturges By Authority: Government Printer, Tasmania 00000 INTRODUCTION To His Excellency Mr Richard William Butler, Companion of the Order of Australia, Governor in and over the State of Tasmania and its Dependencies in the Commonwealth of Australia. MAY IT PLEASE YOUR EXCELLENCY The Committee has investigated the following proposal: - West Tamar Highway, Cormiston Road to Legana (Legana Park Drive), Highway Duplication and now has the honour to present the Report to Your Excellency in accordance with the Public Works Committee Act 1914. Background The planning for the construction of a dual carriageway on the West Tamar Highway from the end of the existing dual carriageway at Cormiston Creek to Legana commenced in the mid 1980’s. In 1992 the Committee gave approval for the first stage of the works to construct a dual carriageway from Cormiston Creek to Danbury Drive (South). Construction works on the first stage of the works (from Cormiston Creek to Danbury Drive (South)) were delayed due to continuing consolidation of the soft sediments on which the dual carriageway was to be built. The consolidation of the soft sediments has been monitored on a continuing basis to determine when the first stage works can be commenced. The delay in the construction of the first stage has now resulted in the proposal that both the first and second stages (Danbury Drive (South) to Legana) be constructed together. This eliminates the need for temporary staging works. In addition, works between Cormiston Road and Cormiston Creek have been included in the project in order to improve the safety for road users on this section of highway. The usage and design standards for this highway have changed considerably since the approval of 1992. The design for the dual carriageway has been revised to reflect the current requirements and design standards. This has resulted in an increase in the estimated construction and total project costs and is a substantial change from what was originally approved by the Committee in 1992. Project Objective The objectives of the project are as follows: • Upgrade the West Tamar Highway to a four lane dual carriageway from Cormiston Creek to Legana (Legana Park Drive) • Make provisions for cycle traffic on the Highway 1 • Rationalise accesses onto the Highway where possible • Improve safety • Improve junction turning facilities PROJECT JUSTIFICATION The significant justifications for this project are the traffic conditions on the highway and at the junctions and safety for road users including recreational cyclists. These main issues are discussed in detail as follows. Traffic The most recent traffic count on this section of the West Tamar Highway was conducted in June 2001 and indicated an Average Annual Daily Traffic (AADT) of 10200 vehicles per day. The AADT in 1990 was 7500 vehicles per day, which represents a growth rate of 3% from 1990 to 2001. The peak hour traffic volume in June 2001 was measured as 1128 vehicles per hour (AM peak with a 78%/22% directional split). Using the 2001 traffic count results and allowing for an average growth rate of 3% gives a current peak hour traffic volume of 1230 vph. This volume of traffic on the existing highway exceeds the volume of traffic for a Level of Service D (LoS D traffic volume 1093 vph). The Austroads Guide to Traffic Engineering Practice Part 2 – Roadway Capacity states “Level of Service D is close to the limit of stable flow and is approaching unstable flow. All drivers are severely restricted in their freedom to select their desired speed and to manoeuvre within the traffic stream. The general level of comfort and convenience is poor, and small increases in traffic flow will generally cause operational problems.” This level of service on the highway results in significant difficulties and delays in accessing the highway from any side roads or accesses. At a growth rate of 3% it is expected that the highway will be at capacity (LoS E) by the year 2016. A four lane dual carriageway highway as proposed would provide a Level of Service A with the current traffic volumes. At a growth rate of 3% the traffic volumes on the four lane dual carriageway highway would reach a Level of Service D in 42 years or by 2046. Safety There have not been a significant number of accidents on this section of the West Tamar Highway for the past several years. However, it is expected that with the decreasing Level of Service being provided by the existing two-lane two-way highway, there will be a rapid increase in the number of accidents and accident severity. The construction of dual carriageway and turning facilities at junctions and accesses would improve the safety on this section of highway. 2 This section of the West Tamar Highway is used extensively by cyclists for training and recreational purposes. The existing highway provides approximately 1.0m wide sealed shoulder adjacent to the 3.0m wide through lanes within a 100km/hr speed zone. This is not considered to be a safe facility for cyclists as there is very little width for motorists to manoeuvre to avoid a cyclist and the air turbulence caused by larger vehicles can result in cyclists losing control and possibly entering the path of following vehicles. The construction of dual carriageway with 3.5m lanes and a 2.0m sealed shoulder would provide a significant improvement in safety for cyclists. THE PROJECT Proposed Works The project involves upgrading the West Tamar Highway to four lane dual carriageway from the end of the existing dual carriageway at Cormiston Creek through to Legana (Acropolis Drive). The four lane dual carriageway tapers back to two lanes at a new single lane roundabout at Acropolis Drive. To the north of the new roundabout the lanes converge back to a single carriageway to tie into the existing highway. The design of this tie in allows for future road widening works through Legana. The new roundabout at Acropolis Drive will provide improved accessibility to the Legana Park Industrial Estate with the construction of a new access road from the roundabout to the existing road within the industrial estate. The roundabout design has been approved by the DIER Chief Traffic Engineer. The upgrading of the highway includes upgrading the turning facilities at junctions. Right turn deceleration lanes and left turn facilities are included for the junctions with Danbury Drive (South) and Danbury Drive (North) as well as at the accesses at Ch.340, Ch.1500 and the Tamar Island Wetland. The project includes the construction of a right turn deceleration lane for south bound traffic at the Cormiston Road intersection. Also included is the widening of the existing north bound carriageway between Cormiston Road and Cormiston Creek to provide a sealed shoulder as well as upgrading the safety barriers to the current standards. This section of the Highway is used extensively by cyclists for training and recreational purposes. The project includes a 2.0m sealed shoulder, which will provide a facility for the use of cyclists. To allow for the road works some services will require relocation including Aurora overhead power lines, Telstra fibre optic and copper cables and an Esk Water water main. Typical Cross Section of the Design The typical cross section on which the design is based provides two 3.5m lanes on each carriageway, a 2.0m sealed shoulder on the outside and 1.0m sealed shoulder on the inside of each carriageway. The verges on the outside of each carriageway are 0.5m, which is widened to 1.0m where safety barrier is required. 3 The median is a constant width along the full length of the highway to produce an improved visual appearance. Where left turn lanes are provided, the turning lane is 3.0m wide and shoulder width has been reduced to 1.0m. Where right turn lanes are provided in the median the turn lanes are 3.5m wide. A kerbed and paved median with safety barrier is provided between the turning lane and the opposing fast lane. Horizontal Alignment The horizontal alignment has been designed to fit the dual carriageway within the existing road reserve and on the surcharge embankment. This has provided very little flexibility in the alignment. Where possible the alignment has been selected to maximise the reuse of the existing pavement. The landform consists of low lying river flats and gentle rolling hills and design speed of the horizontal curves have been achieved in excess of 100km/hr. Vertical Alignment The vertical alignment of the existing Highway is generally very flat. Some local deformations as a result of settlement in the embankment are expected with time between Cormiston Creek and Danbury Drive (South). A minimum level for the Highway has been set at 3.4m, which provides 0.3m of freeboard to the bottom of the pavement for a flood in the Tamar River of one in one hundred year occurrence. There is a slight rise and crest to the north of Danbury Drive (South), the vertical curves associated with this have large radii with a design speed in excess of 100km/hr. The vertical alignment of the design has been chosen to maximise the reuse of the existing pavement while removing deformations arising from settlement in the surcharge embankment.